EP-A-435670 illustrates base oils containing between 65.1 and 69.5 wt % of iso-paraffins and monocyclic naphthene compounds in its saturates fraction and having a pour point of −15° C. This publications also teaches that a high content of these compounds is desirable because they contribute greatly to increased viscosity index and resistance to oxidation.
Known from WO-A-0014179, WO-A-0014183, WO-A-0014187 and WO-A-0014188 are lubricant base stock comprising at least 95 wt % of non-cyclic isoparaffins. WO-A-0118156 describes a base oil derived from a Fischer-Tropsch product having a naphthenics content of less than 10%. Also the base oils as disclosed in applicant's patent applications EP-A-776959 or EP-A-668342 have been found to comprise less than 10 wt % of cyclo-paraffins. Applicants repeated Example 2 and 3 of EP-A-776959 and base oils were obtained, from a waxy Fischer-Tropsch synthesis product, wherein the base oils consisted of respectively about 96 wt % and 93 wt % of iso- and normal paraffins. Applicants further prepared a base oil having a pour point of −21° C. by catalytic dewaxing a Shell MDS waxy Raffinate (as obtainable from Shell MDS Malaysia Sdn Bhd) using a catalyst comprising synthetic ferrierite and platinum according to the teaching of EP-A-668342 and found that the content of iso- and normal paraffins was about 94 wt %. Thus these prior art base oils derived from a Fischer-Tropsch synthesis product had at least a cyclo-paraffin content of below 10 wt %. Furthermore the base oils as disclosed by the examples of application WO-A-9920720 will not comprise a high cyclo-paraffin content. This because feedstock and preparation used in said examples is very similar to the feedstock and preparation to prepare the above prior art samples based on EP-A-776959 and EP-A-668342.